K2-18

Red dwarf star in the constellation Leo

K2-18

Artist's impression of the K2-18 system, with K2-18 on left, K2-18b on right, and K2-18c between.
Credit: ESA/Hubble

Approximate two-dimensional location of the star (in red circle); Sigma Leonis is the nearest bright star, which is in a southerly direction, and the boundary of Virgo is similarly far.

Observation data
Epoch J2000.0 Equinox J2000.0
Constellation | Leo
Right ascension | 11h 30m 14.518s[1]
Declination | +07° 35′ 18.26″[1]
Apparent magnitude (V) | 13.50[2]
Characteristics
Evolutionary stage | Red dwarf
Spectral type | M2.8[3]
Astrometry
Proper motion (μ)|  RA: −80.377[1] mas/yr
Dec.: −133.142[1] mas/yr
Parallax (π)| 26.2686 ± 0.0546 mas[1]
Distance| 124.2 ± 0.3 ly
(38.07 ± 0.08 pc)
Details
Mass| 0.495[4] M☉
Radius| 0.469[4] R☉
Luminosity| 0.0234[5] L☉
Temperature| 3,503[4] K
Metallicity [Fe/H]| 0.123±0.157[6] dex
Other designations

EPIC 201912552, UCAC4 488-054338, 2MASS J11301450+0735180

Database references
SIMBAD| data

K2-18, also known as EPIC 201912552, is a red dwarf star located 124 light-years (38 pc)[4] from Earth, in the constellation of Leo.

## Planetary system[edit]

The star has an exoplanet, called K2-18b, a super-Earth located within the habitable zone of K2-18.[7][8] It is the first exoplanet in the habitable zone, albeit a hydrogen-rich sub-neptune,[9] to have water discovered in its atmosphere. The star also has a second planet K2-18c,[10] which is proven by system tidal simulation to be a small gas giant.[11]

The K2-18 planetary system[11] Companion
(in order from star) | Mass | Semimajor axis
(AU) | Orbital period
(days) | Eccentricity | Inclination | Radius

|
|
|
|
|
|

c | 5.62±0.84 M🜨 | 0.0670 ± 0.0002  | 8.962±0.008  | <0.2  | —  | —
b | 8.63±1.35 M🜨 | 0.1591±0.0004  | 32.94488±0.00281  | —  | —  | 2.711±0.065 R🜨

## References[edit]

1. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
2. ^ Zacharias, N.; Finch, C. T.; Girard, T. M.; Henden, A.; Bartlett, J. L.; Monet, D. G.; Zacharias, M. I. (2012). "VizieR Online Data Catalog: UCAC4 Catalogue (Zacharias+, 2012)". VizieR On-line Data Catalog. Bibcode:2012yCat.1322....0Z.
3. ^ Montet, Benjamin T.; et al. (5 August 2015). "Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation". The Astrophysical Journal. 809 (1): 25. arXiv:1503.07866. Bibcode:2015ApJ...809...25M. doi:10.1088/0004-637X/809/1/25. S2CID 33348734.
4. ^ a b c d Cloutier, Ryan; et al. (7 January 2019). "Confirmation of the radial velocity super-Earth K2-18c with HARPS and CARMENES". Astronomy & Astrophysics. 621. A49. arXiv:1810.04731. Bibcode:2019A&A...621A..49C. doi:10.1051/0004-6361/201833995. S2CID 118828975.
5. ^ Martinez, Arturo O.; Crossfield, Ian J. M.; Schlieder, Joshua E.; Dressing, Courtney D.; Obermeier, Christian; Livingston, John; Ciceri, Simona; Peacock, Sarah; Beichman, Charles A.; Lépine, Sébastien; Aller, Kimberly M.; Chance, Quadry A.; Petigura, Erik A.; Howard, Andrew W.; Werner, Michael W. (2017). "Stellar and Planetary Parameters for K2's Late-type Dwarf Systems from C1 to C5". The Astrophysical Journal. 837 (1): 72. arXiv:1701.00588. Bibcode:2017ApJ...837...72M. doi:10.3847/1538-4357/aa56c7. S2CID 25502982.
6. ^ Benneke, Björn; Werner, Michael; Petigura, Erik; Knutson, Heather; Dressing, Courtney; Crossfield, Ian J. M.; Schlieder, Joshua E.; Livingston, John; Beichman, Charles; Christiansen, Jessie; Krick, Jessica; Gorjian, Varoujan; Howard, Andrew W.; Sinukoff, Evan; Ciardi, David R.; Akeson, Rachel L. (2017). "Spitzer Observations Confirm and Rescue the Habitable-zone Super-Earth K2-18b for Future Characterization". The Astrophysical Journal. 834 (2): 187. arXiv:1610.07249. Bibcode:2017ApJ...834..187B. doi:10.3847/1538-4357/834/2/187. S2CID 12988198.
7. ^ "HABITABLE EXOPLANETS CATALOG". UPR. 7 March 2016. Retrieved 12 September 2019.
8. ^ "EPIC 201912552 b reality check drewexmachina 11-22-2015". Drew ExMachina. 7 March 2016. Retrieved 12 September 2019.
9. ^ No, the Exoplanet K2-18b Is Not Habitable
10. ^ "EPIC 201912552". Open Exoplanet Catalogue. 7 March 2016. Retrieved 12 September 2019.
11. ^ a b Ferraz-Mello, S.; Gomes, G. O. (2020). "Tidal evolution of exoplanetary systems hosting potentially habitable exoplanets. The cases of LHS-1140 b-c and K2-18 b-c". Monthly Notices of the Royal Astronomical Society. 494 (4): 5082–5090. arXiv:2005.10318. Bibcode:2020MNRAS.494.5082G. doi:10.1093/mnras/staa1110. S2CID 218763252.

* v
* t
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Constellation of Leo

* List of stars in Leo
* Leo in Chinese astronomy

Stars|

| Bayer|

* α (Regulus)
* β (Denebola)
* γ (Algieba)
* δ (Zosma)
* ε (Algenubi)
* ζ (Adhafera)
* η
* θ (Chertan)
* ι
* κ (Al Minliar al Asad)
* λ (Alterf)
* μ (Rasalas)
* ν
* ξ
* ο (Subra)
* π
* ρ
* σ
* τ
* υ
* φ
* χ
* ψ
* ω

|

Flamsteed|

* 3
* 6 (h)
* 7
* 8
* 9
* 10
* 11
* 12
* 13
* 15 (f)
* 18
* 19
* 20
* 21
* 22 (g)
* 23
* 26
* 31 (A)
* 33
* 34
* 35
* 37
* 39
* 40
* 42
* 43
* 44
* 45
* 46
* 48
* 49
* 50
* 51 (m)
* 52 (k)
* 53 (l)
* 54
* 55
* 56
* 57
* 58 (d)
* 59 (c)
* 60 (b)
* 61 (p2)
* 62 (p3)
* 64
* 65 (p4)
* 66
* 67
* 69 (p5)
* 71
* 72
* 73 (n)
* 75
* 76
* 79
* 80
* 81
* 82
* 83
* 85
* 86
* 87 (e)
* 88
* 89
* 90
* 92
* 93
* 95 (o)
* 6 LMi
* 18 LMi
* 49 LMi
* 52 LMi
* 10 Sex
* 11 Sex
* 37 Sex

Variable|

* R
* S
* X
* Y
* RR
* RZ
* SS
* ST
* TU
* TV
* UV
* UZ
* XY
* XZ
* AD
* AM
* AP
* AQ
* CE
* CN
* CW
* DH
* DK
* DN
* DP
* DR
* DX
* DY
* EE
* EO
* EX
* GX
* HN

HR|

* 3736
* 3792
* 3804
* 3820
* 3869
* 3876
* 3942
* 3969
* 4006
* 4012
* 4032
* 4048
* 4097
* 4197
* 4244
* 4245
* 4249
* 4253 (p1)
* 4303
* 4341
* 4358
* 4394
* 4404
* 4419
* 4459 (Formosa)
* 4465
* 4512
* 4531
* 4535
* 4543

HD|

* 81040
* 84680
* 86986
* 88133
* 89307
* 95089
* 96063 (Dingolay)
* 96372
* 97658
* 99109 (Shama)
* 100456
* 100659
* 100777 (Sagarmatha)
* 102272

Other|

* BD+20 2457
* Gliese 408
* Gliese 410
* Gliese 436
* GJ 3685
* HVS 7
* K2-3
* K2-18
* 2MASSI J0937347+293142
* 2MASS J10475385+2124234
* MACS J1149 Lensed Star 1
* PG 1031+234
* PSR B0919+06
* PSR B0943+10
* PSR B0950+08
* PSR B1133+16
* PSR J1022+1001
* SDSS J102915+172927
* WD 1105-048

| Exoplanets|

* γ1 Leonis b
* Mu Leonis b
* DP Leonis b
* GJ 436 b
* HD 81040 b
* HD 88133 b
* HD 87646 b
* HD 89307 b
* HD 89345 b
* HD 94834 b
* HD 95089 b
* c
* HD 96063 b
* HD 97658 b
* HD 98736 b
* HD 99109 b
* HD 100655 b
* HD 100777 b
* HD 102272 b
* c
* WASP-104 b
* WASP-106 b
* WASP-183 b

|

Galaxies|

| Messier|

* 65
* 66
* 95
* 96
* 105

|

NGC|

* 2903
* 2906
* 2964
* 3041
* 3048
* 3185
* 3190
* 3226
* 3227
* 3239
* 3274
* 3301
* 3357
* 3367
* 3370
* 3377
* 3384
* 3412
* 3426
* 3455
* 3489
* 3501
* 3506
* 3521
* 3593
* 3596
* 3598
* 3599
* 3602
* 3605
* 3607
* 3608
* 3608
* 3608
* 3608
* 3608
* 3608
* 3608
* 3697
* 3705
* 3805
* 3810
* 3816
* 3821
* 3837
* 3840
* 3841
* 3844
* 3845
* 3851
* 3857
* 3859
* 3860
* 3861
* 3862
* 3864
* 3867
* 3868
* 3873
* 3875
* 3883
* 3884
* 3886
* 3902
* 3925
* 3937

Numbered|

* I
* II
* III
* IV
* V

Category

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*[RA:]: Right Ascension
*[Dec.:]: Declination
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